Date Published: August 11, 2014
Publisher: Public Library of Science
Author(s): Ai Takano, Kochi Toyomane, Satoru Konnai, Kazuhiko Ohashi, Minoru Nakao, Takuya Ito, Masako Andoh, Ken Maeda, Masahisa Watarai, Kozue Sato, Hiroki Kawabata, Brian Stevenson.
During 2012–2013, a total of 4325 host-seeking adult ticks belonging to the genus Ixodes were collected from various localities of Hokkaido, the northernmost island of Japan. Tick lysates were subjected to real-time PCR assay to detect borrelial infection. The assay was designed for specific detection of the Relapsing fever spirochete Borrelia miyamotoi and for unspecific detection of Lyme disease-related spirochetes. Overall prevalence of B. miyamotoi was 2% (71/3532) in Ixodes persulcatus, 4.3% (5/117) in Ixodes pavlovskyi and 0.1% (1/676) in Ixodes ovatus. The prevalence in I. persulcatus and I. pavlovskyi ticks were significantly higher than in I. ovatus. Co-infections with Lyme disease-related spirochetes were found in all of the tick species. During this investigation, we obtained 6 isolates of B. miyamotoi from I. persulcatus and I. pavlovskyi by culture in BSK-M medium. Phylogenetic trees of B. miyamotoi inferred from each of 3 housekeeping genes (glpQ, 16S rDNA, and flaB) demonstrated that the Hokkaido isolates were clustered with Russian B. miyamotoi, but were distinguishable from North American and European B. miyamotoi. A multilocus sequence analysis using 8 genes (clpA, clpX, nifS, pepX, pyrG, recG, rplB, and uvrA) suggested that all Japanese B. miyamotoi isolates, including past isolates, were genetically clonal, although these were isolated from different tick and vertebrate sources. From these results, B. miyamotoi-infected ticks are widely distributed throughout Hokkaido. Female I. persulcatus are responsible for most human tick-bites, thereby I. persulcatus is likely the most important vector of indigenous relapsing fever from tick bites in Hokkaido.
Borrelia miyamotoi, a member of the relapsing fever group (RF) borreliae, was first discovered from Ixodes persulcatus ticks and the rodent, Apodemus argenteus, in Hokkaido, the northernmost island of Japan . Subsequently, B. miyamotoi has been found in Ixodes scapularis and Ixodes pacificus ticks in North America , ,  and Ixodes ricinus in Europe , . Cases of human infections with B. miyamotoi were initially reported in Russia . Following this report, several human cases have been confirmed as B. miyamotoi infections in North America ,  and Europe . Recently, tick surveillance for B. miyamotoi was performed in Europe  and Russia . The surveys showed that I. ricinus and I. persulcatus in the Eurasian continent consistently harbor B. miyamotoi with low prevalence. However, large-scale tick surveillance has not been conducted in Asian countries where I. persulcatus is distributed.
It is known that I. persulcatus principally serves as a tick vector for LD borreliae in Hokkaido. Hokkaido has an area of approximately 83,000 km2, and the total population of Hokkaido, according to the National Census 2010, is 5.5 million people (http://www.stat.go.jp/english/index.htm). However, 42% of the population inhabits the plains of Ishikari district (Figure 1). Similar to the taiga zone in Russia, I. persulcatus ticks are abundant mainly in forested areas of northern and eastern Hokkaido, which are thinly populated. Human tick bites and tick-borne LD, therefore, occur sporadically in Hokkaido . In this study, we conducted large-scale tick surveillance for B. miyamotoi in Hokkaido, because human cases of B. miyamotoi infections have been confirmed in Russia . Moreover, human B. miyamotoi infection, determined through retrospective analysis, has been reported in Hokkaido (http://www.nih.go.jp/niid/ja/relapsing-fever-m/relapsing-fever-iasrs/3877-pr4046.html). Our study demonstrated that B. miyamotoi is widely distributed throughout Hokkaido with low prevalence (0–3%) in I. persulcatus (Table 1, Figure 2). The prevalence is similar to those reported in Russian and European I. persulcatus, . Besides I. persulcatus, B. miyamotoi was found from 4.3% (within 0–6.1%) of I. pavlovskyi, and this is the first report of detection and isolation of B. miyamotoi from I. pavlovskyi. Moreover, we detected B. miyamotoi from an I. ovatus male. However, given that the prevalence in I. ovatus was significantly lower than that in I. persulcatus and I. pavlovskyi, the potential vectors of B. miyamotoi in Hokkaido are thought to be I. persulcatus and I. pavlovskyi. Female ticks of I. persulcatus are responsible for most human tick-bites in Hokkaido . The abundance of B. miyamotoi-infected female ticks is, therefore, directly linked to human risk. Although the prevalence of B. miyamotoi is relatively low in rural communities of Hokkaido, B. miyamotoi is important for public health as an agent of fever and variable symptoms. Moreover, I. pavlovskyi can serve as an additional vector for B. miyamotoi. I. persulcatus and I. pavlovskyi are closely related morphologically, ecologically and phylogenetically , . The larvae and nymphs of both tick species have a wide range of feeding hosts, such as small mammals and birds. On the other hand, unlike I. persulcatus, adult I. pavlovskyi mainly infests birds. The potential for I. pavlovskyi to bite humans is still unclear, however, its public health significance is negligible given the far lower abundance.